Blazor get nested components by Reflection

问题

I'm actually working on form validation in Blazor project (0.8.0).

I have created a component called InputValidation. This component receive many parameters to test if a property value is correct according a condition we can set up.

@using System.Linq.Expressions;

@typeparam TItem

@if (!Valid)
{
    <span id="@(Id)_validation" class="form-text text-danger">@Message</span>
}

@functions {

    [Parameter]
    string Id { get; set; }

    [Parameter]
    TItem Property { get; set; }

    [Parameter]
    Expression<Func<TItem, bool>> On { get; set; }

    [Parameter]
    string Message { get; set; }

    [Parameter]
    bool ActiveOnLoad { get; set; } = true;

    internal bool Valid { get; set; }
    bool Activated;

    protected async override Task OnInitAsync()
    {
        Activated = ActiveOnLoad;
    }

    protected async override Task OnAfterRenderAsync()
    {
        Activated = true;
    }

    protected async override Task OnParametersSetAsync()
    {
        Valid = !On.Compile().Invoke(Property);
    }
}

You can implement it on your parent component like this :

<InputValidation Id="@nameof(ViewModel.UrlInput)" Property="@ViewModel.UrlInput" On="@(x => string.IsNullOrEmpty(x))" Message="Url is empty" ActiveOnLoad="@false"/>

I have coded a class that verifies that all InputValidation components have the property Valid at true.

@if (ViewModel.IsValid(this))

this represents the parent component.

The problem is... it's not working !

Here is the code of the validator :

public static class ModelValidator
{
    public static bool IsValid<T, V>(this T viewmodel, V component) where T : IViewModel where V : ComponentBase
        => component.GetType().GetFields().OfType<InputValidation<T>>().All(x => x.Valid);
}

It's not working, I know, but even if we use Reflection (GetProperties, GetFields, GetMembers), it won't return any of the InputValidation members of the parent component.

My question is : is there a way to get all child components by using Reflection ? If yes, how to do it ?

I know that Blazor is still on early stage and I hope it will be released soon because it's a very pleasant technology !

Thank you for your responses !

回答1:

You don't need reflection here (the InputValidation component is not a field in the parent, it is a component that will be rendered by the RenderTree).

You can capture a reference to each InputValidation component using the ref attribute.

<InputValidation ref="@InputValidationRef" Id="@nameof(ViewModel.UrlInput)" Property="@ViewModel.UrlInput" On="@(x => string.IsNullOrEmpty(x))" Message="Url is empty" ActiveOnLoad="@false"/>

Normally this ref "InputValidationRef" would be a field, but you can, instead use a property with a custom setter to build a list (or whatever collection you like)

List<InputValidation> InputValidations = new List<InputValidation>();
InputValidation InputValidationRef { set => InputValidations.Add(value); }

So, each InputValidation will now be captured as a reference and the Property InputValidationRef will be set for each one, which will, in turn, store all the references in the collection "InputValidations".

Now, you have a collection, you can test against

InputValidations.All(iv => iv.Valid)

Note: the collection is only populated after the component/page is rendered, so during the initial page load the collection of references is empty until the OnAfterRender/OnAfterRenderAsync method is called.

来源：https://stackoverflow.com/questions/54859217/blazor-get-nested-components-by-reflection

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ASP.NET

razor

asp.net-core

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